Method for replacing worn or fractured teeth on large gear rings



Sept. 20, 1966 c, ROYER 3,273,232

METHOD FOR REPLACING WORN OR FRACTURED TEETH ON LARGE GEAR RINGS Filed Oct. 21, 1965 4 Sheets-Sheet 1 INVENTOR. 62.407 4/ Furs-E Sept. 20, 1966 3,273,232

METHOD FOR REPLACING WORN OR FRACTURED TEETH ON LARGE GEAR RINGS Filed Oct. 21, 1965 c. J. 'ROYER 4 Sheets-Sheet 2 Tics-"1 FLEE INVENTOR. 62 40? d6 Peri-A BY g ATTOAA/EYS j Se t. 20, 1966 c. J. ROYER 3,273,232

METHOD FOR REPLACING WORN 0H FRACTURED TEETH ON LARGE GEAR RINGS Filed Oct. 21. 1965 4 Sheets-Sheet 5 INVENTOH. Cmor d. Pave-Q METHOD FOR REPLACING WORN 0R FRACTURED TEETH 0N LARGE GEAR RINGS Filed Oct. 21, 1965 C. J. ROYER Sept. 20, 1966 4 Sheets-Sheet 4 TEJLEi-LL m w J \AL r 5 \d JZ MH P/ aw 6 5 M 0 2 M 5 6 T 1. Elm

INVENTOR. 624m 4/, Pare-e United States Patent Oil ice 3,273,232 Patented Sept. 20, 1966 3,273,232 METHOD FOR REPLACING WORN R FRAC- TURED TEETH 0N LARGE GEAR RINGS Clady J. Royer, 2645 NW. 26th St., Oklahoma City, Okla. Filed Oct. 21, 1965, Ser. No. 499,200 11 Claims. (Cl. 29401) This invention relates to a method for replacing worn or fractured teeth on large gear rings or gear circles and is a continuation-in-part of my co-pending application Serial No. 391,162, filed August 24, 1964. More particularly, the present invention relates to a method for quickly and easily replacing a plurality of the teeth used in a gear circle of the specific type employed in large graders and other earth-moving equipment.

In earthmoving vehicular equipment of the type typified by the road grader manufactured by the Caterpillar Company of Peoria, Illinois, the vehicle is generally provided with a large grader blade which extends transversely across and beneath the frame of the vehicle, and is secured to a large ring gear or a gear circle of some 4 to 7 feet in diameter. The gear circle is engaged by a pinion and may be rotated thereby to change the angle formed by the grader blade with respect to the longitudinal axis of the vehicle frame. The gear circle is normally supported by a plurality of circle guide shoes which are generally right angularly shaped structures having a toe portion which extends beneath, and supports in a generally horizontal plane, the gear circle, and also having a vertically extending portion which acts as a guide to assist in maintaining the position of the gear circle relative to a vertical axis passing through the center thereof. The teeth of the gear circle extend radially inwardly toward the vertical axis of the circle and contact the upper surface of the horizontally extending toe portion of the circle guide shoes. The vertically extending, radially inner edges of the teeth of the gear circle frequently bear against, or come in contact with, the vertically extending portions of the guide shoes so that some wear results at the vertically extending, radially inner edges of the teeth during operation of the earthmoving vehicle.

The large gear circle used in vehicles of the type described is usually further characterized in having a downwardly extending circumferential flange formed on the outer periphery thereof and a right angular or L- shaped brace which is welded at the edge of a horizontally extending leg thereof to the lower edge of the downwardly extending circumferential flange, and at the upper edge of the upwardly extending leg thereof to the lower surface of the gear circle. The function of the L- shaped brace is to enhance the structural strength and mechanical rigidity of the gear circle.

In the operation of earthmoving vehicles of the type described, very large mechanical loads are frequently imposed upon the grader blade and transmitted through the moldboard and other connecting structure to the gear circle. These loads are frequently unevenly distributed along the blade with the result that unequal stresses are transmitted through the moldboard and connecting structure to the gear circle, and ultimately to the gear teeth of the circle. The sudden impact imparted to the blade when it strikes buried rock or other impacted, relatively difficultly moved structure also severely stresses the gear circle teeth. The loading of the teeth as thus imposed, coupled with the frictional wear and abrasion produced by the constant wear of the teeth against the supporting and guiding surfaces of the circle guide shoes results in the teeth becoming worn away to the extent that they do not mesh properly with the driving pinion gear, and

do not guide on, or ride smoothly over, the circle guide shoes. In some instances, some of the teeth may even be sheared off or fractured. In any event, an unacceptably high degree of wear or deterioration of some of the gear teeth always occurs before the end of the useful life of the remaining gear circle structure so that it is more desirable to replace only the worn or fractured teeth rather than replacing the entire gear circle.

Another problem which arises from the uneven distribution of loads imposed on the gear circle during gradmg operations is that the gear circle will ultimately become distorted from its true round configuration to a slightly elliptical or oval configuration. This distortion of the gear circle results from the propensity of grader op erators to incline the grader blade at the same angle with respect to the frame of the vehicle during all grading operations so that a continuous load is imposed on one segment of the gear circle tending to distort the circle in the same direction.

The desirability or need for replacing worn or lost teeth on various types of annular structures, such as cogs, sprockets and gears, as opposed to replacing the entire or complete gear, exists in many types of mechanical structures, and various methods for accomplishing such replacement have been previously proposed and carried out with varying degrees of success. Where the structure comprises an annular member supported on spokes or a spider extending radially from a hub, it has been proposed to make the tooth-carrying annular member in segments which can be detachably secured to the spokes or spider and individually replaced when required. This procedure, which is typified by the disclosures of Shores US. Patent 2,285,225, Melone US. Patent 3,111,859, and Dawe et al. US. Patent 3,083,585, has the advantage of permitting only a portion of the entire sprocket or gear combination to be replaced when the teeth become worn, but is limited to use in structures having some type of radial support, such as spokes or the like, for the annular segments. Moreover, in replacing an entire annular segment, including not only the teeth which it is desired to renew, but also the base structure which supports and carries the teeth, the cost is higher than in the case of replacement of only the individual worn teeth, and the tooth supporting structure which is discarded with the replaced segments is merely wasted, since it is usually not worn or damaged in any way.

Since in the gear circles used in large earthmoving vehicles or graders, and of the type hereinbefore described, there are no spokes or other radial supporting structure, the method of replacing entire segments of the annular portion of the gear circle by detachment from the spokes cannot be employed. Instead, the older and well-known method of tooth replacement is employed in which the individual worn or fractured teeth are individually removed and painstakingly replaced. This procedure, one form of which is described in US. Patent 1,406,110 to Troutner is timeaconsuming and expensive, and requires the employment of a highly skilled welder. Even using welders of high skill, it is frequently very diificult to procure the desired alignment and geometric relationship between the replacement teeth and those which have not been replaced.

The present invention contemplates a novel method for replacing the worn or fractured teeth on a gear circle of the type used in large earthmoving or grader type vehicles. As previously described, these vehicles have a large grader blade extending transversely across the vehicle beneath the frame thereof and supported by a large circular gear ring having radially inwardly projecting teeth. These teeth are engaged by a pinion for driving the gear circle in rotation to adjust the angular position of the grader blade. The invention is specifically applicable to wheeled graders of the type having a grader blade mounted on or suspended beneath a large metallic gear ring or circle, which gear circle is supported and guided by a plurality of guide shoes which bear against the teeth of the gear circle and function-to support the gear circle and maintain it in a position for meshing with the driving pinion.

The invention is particularly useful and applicable to gear circles of the described type which have been distorted from their true circular configuration by long usage in grader vehicles in which the grader blade has been continuously extended at substantially the same angle.

Broadly described, the present invention comprises initially forming a plurality of toothed segments which are identical in geometric configuration to corresponding arcuate segments of the gear circle upon which are located the worn or defective teeth to be replaced, as such arcuate segments were configured at the time the gear circle was new. In other words, the toothed segments which are initially formed in the practice of the present invention are segments of a true circle, and the teeth which are carried by these segments are identical in geometric configuration to the unworn or new teeth which were carried by the gear circle prior to wear and deterioration of the teeth. The angular size of the toothed segments which are formed may be varied, but is preferably equivalent to an octant of the gear circle, or 45 of arc. It is very desirable to limit the size of the segments to 45 of are or smaller since the segments, though preferably forged, can be formed by casting, and it is difficult and expensive to cast them in the proper configuration if they are made of larger size than the 45 of are for use in the large gear circles to which the present invention is applicable.

In the next step of the procedure, slots are cut radially outwardly from points disposed between certain adjacent teeth on gear circle toward the outer periphery thereof in order to provide reference slots for centering the old gear circle on a cutting jig used later in the process. The slots which are cut radially outwardly from the teeth of the gear circle are symmetrically disposed around the inner periphery of the gear circle in equally spaced relation to each other, and are preferably at least eight in number. In the most preferred method of carrying out the process of the invention, the slots include, but are not limited to, two pairs of slots which are cut in the gear circle from the base of the teeth on opposite sides of the gear circle with the individual slots in each pair of these slots being spaced from each other by a distance equivalent to the distance measured across the base of two teeth which separate the slots.

After the reference slots have been out in the gear circle in the manner described, a circular, disc-shaped cutting jig is placed on top of the gear circle. The cutting jig has an upper surface and a flat lower surface which bears against the upper surface of the gear circle. The jig is centered on the gear circle by the use of several reference slots which have been cut therein. The outer periphery of the cutting jig which is used has been machined to constitute a perfect circle. Positioned inwardly from the outer periphery of the jig on the upper surface thereof are a plurality of concentric annular slots or grooves which function as tracks for supporting and guiding an automatic, flame cutting machine which is used in the process for cutting away the old gear teeth.

With the cutting jig centered on the gear circle, the flame cutting machine is mounted in the grooves constituting tracks provided on the upper surface of the jig, and the cutting head is set so as to cut through the gear circle radially outwardly from the base of the teeth thereon, and at an angle of about 75 to the flat upper surface of the gear circle. The teeth are thus removed from the gear circle and a beveled surface is provided on the inner periphery of the gear circle where the teeth have been cut away. Since the flame cutting machine moves in a perfect circle on the jig byreason of its guiding on the grooved annular tracks provided in the surface thereof, the cutting head of the flame cutting machine cuts in a perfect circle, and the beveled surface which remains on the inner periphery of the gear circle after removal of the teeth therefrom is also perfectly circular.

It should be pointed out at this point in the discussion that the several arcuate toothed segments which have been constructed and are to be used to replace the worn or fractured teeth are each provided at their outer peripheral, arcuate surfaces with a face which is angled in two planes, with one of these planes extending normal to the upper surface of the respective segment and the other forming an acute angle with the bottom surface of the segment. This permits a gap to be left between the segments and the beveled surface provided on the gear circle after removal of the old teeth therefrom with the flame cutting machine as previously described, and these gaps are utilized for the accommodation of welding material when the new toothed segments are secured to the gear circle at a later time in the process.

When the old teeth have been removed from the gear circle by the use of the circular cutting jig and the flame cutting machine in the manner described, the several arcuate toothed segments carrying the new replacement teeth are supported on the upper surface of the circular cutting jig and adjacent the outer periphery thereof. The several arcuate toothed segments are disposed in the desired position relative to each other by moving the radially inner ends of the teeth inwardly on the jig until they abut against an annular shoulder which is formed on the upper surface of the jig in radially inwardly spaced relation to the outer peripheral edge thereof. The several segments are also spaced slightly from each other in a circumferential direction to accommodate for longitudinal thermal expansion of the several segments as they are welded in place in the course of the process as hereinafter described. By abutting the inner face of the teeth of the new segments against the machined, annular shoulder on the upper face of the cutting jig, the segments collectively form a perfect circle around the jig. The segments are then clamped in place by the use of clamping blocks and cap screws which are extended between the teeth of the segments into threaded holes formed in the upper surface of the cutting jig between the annular shoulder thereon and the outer peripheral edge of the jig. The clamping blocks and cap screws function to firm-1y retain each of the segments in its proper position on the jig and relative to the gear circle during subsequent operations of the process.

With the segments clamped in place in a circular configuration on the cutting jig, the jig is lowered into the gear circle which has had the old teeth removed therefrom as hereinbefore described. Since the outer periphery of the several segments'extend along a perfect circle, and since the beveled surface which has been formed by cutting away the old teeth from the gear circle using the cutting jig is also perfectly circular in configuration, the segments fit uniformly against the beveled surface of the gear circle and are positioned for welding to the gear circle. After the cutting jig and the segments which it carries have been leveled with respect to the gear circle to cornpensate for any distortion from the horizontal plane which may have occurred in the gear circle over an extended period of use, the several segments are welded in place on the gear circle. This is preferably accomplished by initially tack Welding the segments at several points spaced around the entire gear circle on the bottom side of the gear circle. welded to the upper side of the segments.

The process as thus carried out accomplishes the positioning of new gear teeth on the inner periphery of the gear circle with the teeth being perfectly circular in their collective configuration and disposed in a horizontal plane. Moreover, the procedure lends itself to the use of harder and more exotic metal in forging the new teeth on the preformed segments than the type of metal which is used in the gear circle as originally fabricated. Thus, teeth The upper side of the gear circle is then having a longer service life are actually incorporated in the rebuilt gear circle. Also, in incorporating the perfectly round segmented preformed structure within the outer peripheral base structure of the original gear circle, the distorted outer periphery of the gear circle is maintained in this form and therefore tends to resist further distortion. In other words, the distorting influence of uneven loading on the grader blade has been previously imparted to that portion of the gear circle which sustains the greatest portion of the mechanical loading, and in retaining this distorted portion in the rebuilt gear circle, no further distortion of this portion tends to occur, and yet the inner periphery which carries the new teeth is in perfect round and tends to remain that way for the remaining service life of the gear circle.

From the foregoing description of the invention, it will have become apparent that a major object of this invention is to provide a new and improved method for quickly and inexpensively replacing worn or fractured teeth on gear circles of the type used in earthmoving vehicles for supporting the moldboard of grader blades mounted on said vehicles.

Another object of the present invention is to provide a method for replacing the teeth on large gear circles of the type described without the necessity for removing the individual teeth, and then replacing them by a building-up process.

Another object of the present invention is to provide a method for replacing the teeth on large gear circles of the type described without dependence on the individual skill of the welder for cutting away the gear teeth with a cutting torch.

An additional object of the present invention is to provide a method for replacing worn teeth on the inner periphery of a large gear circle of the type used in earthmoving vehicles carrying large grader blades which extend transversely of the vehicle and beneath the frame thereof, which method facilitates replacement of the worn teeth with teeth which are constructed of harder and more mechanically desirable types of metal than the teeth origtinally used in such gear circles.

Yet another object of the present invention is to provide a method for replacing worn or fractured teeth in large gear circles of the type used on motor graders, which method permits an out-of-round or distorted condition of such gear circles to be compensated, and the replacement teeth incorporated thereon to be positioned around the inner periphery of the gear circle in a perfect circle.

Another object of the present invention is to provide a method for replacing the teeth located at the inner periphery of a large gear circle of the type used on motor graders, with such method tending to prevent subsequent distortion of the tooth bearing portion of the gear circle from a true circular configuration.

In addition to the foregoing described objects and advantages, other objects and advantages will become apparent as the following detailed description of the invention is read in conjunction with a perusal of the accompanying drawings which illustrate the invention.

In the drawings:

FIGURE 1 is a perspective view of a large gear circle of the type utilized on motor graders as such a gear circle appears prior to the removal of the old teeth therefrom and at the outset of the process of the present invention. FIGURE 1 also illustrates the reference slots which are cut radially outwardly from the base of several of the gear teeth in the gear circle for the purpose of facilitating the alignment of the circular cutting jig on the gear circle.

FIGURE 2 is a plan view of the gear circle illustrated in FIGURE 1 and showing the circular or disc-shaped cutting jig as it appears when superimposed on the gear circle and aligned thereon by the use of the reference slots which have been cut in the gear circle.

FIGURE 3 is a sectional view taken along line 33 of FIGURE 2.

FIGURE 4 is a perspective view of the gear circle with the cutting jig mounted thereon, and an automatic flame cutting machine supported in annular track grooves formed on the upper surface of the cutting jig. The cutting head of the flame cutting machine is extended at the optimum angle with respect to the gear circle for cutting the teeth therefrom to provide a beveled inner peripheral surface.

FIGURES 5, 6 and 7 are views illustrating one of the arcuate toothed segments which are forged for use in the process of the present invention as replacements for the worn gear teeth removed from the gear circle.

In FIGURE 5, one of the segments is shown in elevation corresponds to an octant of the entire .gear circle in its angular dimension.

FIGURE 6 is a sectional view taken along line 6-6 of FIGURE 5.

FIGURE 7 is a view in elevation of one end of the preformed toothed segment as the segment appears when viewed horizontally at one end thereof.

FIGURE 8 is a perspective view showing the appearance of the cutting jig with the several preformed segments mounted around the outer periphery of the cutting jig using clamping blocks and cap screws for holding the segments in position.

FIGURE 9 is a perspective view illustrating the step of the process in which the circular cutting jig carrying the several preformed toothed segments thereon is positioned inside the gear circle in inverted relation to its position shown in FIGURE 8 after the old gear teeth have been cut therefrom.

FIGURE 10 is a sectional view taken along line 10--10 of FIGURE 9 and illustrating the relationship of one of the gear segments to the gear circle and the cutting jig immediately prior to welding the segments to the gear circle.

FIGURE 11 is a perspective view showing the gear circle with the cutting jig carrying the several preformed toothed gear segments retained in proper position thereon after the gear circle has been inverted to permit the under side of the segments to be welded to the gear circle.

Referring to the drawings in detail, and particularly, to FIGURE 1, the specific type of ring gear or gear circle to which the invention can most beneficially be applied is of the type which is typically mounted upon a large motor grader, and which is illustrated in perspective in FIGURE 1. The gear circle is designated generally by reference character 10 and includes a flat, annular metallic member 12 which is adapted to be supported by a plurality of circle guide shoes of the type used on a motor grader which function to guide and maintain the annular metallic member in alignment about a vertical axis passing through the center of the gear circle. The gear circle 10 is provided with a pair of horizontally spaced, downwardly depending moldboard support structures 14 which are utilized for mounting a grader blade on the motor grader as is well understood in the art. At the inner periphery of the annular metallic member 12, a plurality of radially inwardly extending equi-sized gear teeth 16 are provided and are positioned, when the gear circle is newly fabricated, on the outer periphery of a circle.

As best illustrated in FIGURES l and 3, the gear circle 10 is further characterized in having a downwardly extending circumferential flange 18 which is secured to the outer peripheral edge of the annular metallic member 12. The flange 18 is welded or otherwise suitably secured adjacent its lower edge to the horizontally extending leg 20 of an Lshaped brace designated generally by reference character 22. The Lshaped brace also includes an upwardly extending leg 24 which is secured to the under side of the annular metallic member 12 at a position relatively close to the tooth-carrying inner peripheral edge of the annular metallic member. It is to be understood that though the brace 22 has been described as L-shaped in referring to the sectional view of FIGURE 3, this configuration represents the shape of the brace only in transverse cross-section, and the brace in its entirety is actually an annular member having a horizontally extending leg and a vertically or upwardly extending leg 24. Thus, the line of intersection between the radially inner face of the leg 24 of the brace 22 with the under surface of the annular metallic member 12 is actually a circular line which is position intermediate the inner and outer peripheries of the annular metallic member.

Under the conditions giving rise to the use of the present invention, one or more of the gear teeth 16 may become severely worn to the point where the teeth do not mesh well with the driving pinion on the motor grader in which the gear circle is mounted, or do not ride smoothly over the circle guide shoes which support the gear circle. In most instances, wearing will be pronounced over a certain localized area of the gear circle and will involve a plurality of the teeth 16 in that area. Occasionally, one or more of the teeth 16 in the area of greatest wear may become fractured or sheared off between the point of the tooth and the rear or base structure constituted by the annular metallic member 12. When such wear and fracturing has progressed to an undesirable extent, it then becomes necessary to remove the worn teeth 16 and replace them with new teeth by a building-up welding process or by some other method. The methods employed in the past have been time consuming and expensive by reason of requiring a highly skilled welder and a particular, rather complicated technique. In many instances, it has been preferable to simply replace the entire gear circle with a new gear circle rather than to undertake to remove the worn teeth.

At the time in the service life of a gear circle 10 when the gear teeth 16 have become worn to the extent described and possibly fractured, the gear circle as a whole has usually become distorted from its true circular configuration as originally constructed by reason of the high and uneven mechanical loads imposed thereon in continuous use as hereinbefore described. For example, if the grader blade carried upon the moldboard support structures 14 is canted at an angle of about 60 with respect to the longitudinal axis of the frame of the grader vehicle, and is continuously used at that angle for grading roads, the loading on the gear circle will be distributed unevenly and a distorting force will continually act on the gear circle to change its configuration to a slightly elliptical or egg-shaped form. It will be seen that a distortion of the gear circle 10 from a true circular configuration will tend to aggravate and further the wear of the teeth 16 carried thereby, since they will then bind more severely on the circle guide shoes as the gear circle is driven in rotation.

In the practice of the present invention, the gear circle 10 carrying the worn teeth 16 is initially removed from the earthmoving vehicle by techniques well understood in the art. A plurality of preformed toothed arcuate segments are then made by forging or other suitable procedure. A typical embodiment of such toothed, preformed gear segments is illustrated in FIGURES 5, 6 and 7 with the segment there shown being designated generally by reference character 30. Each of the segments is formed on a segment of a circle, and the length of each segment may be varied, but preferably is equivalent to a quadrant of a circle or about 45 of arc. The inner periphery of each of the preformed segments 30 carries gear teeth 32 which are identical in geometric configuration and circumferential spacing to the teeth 16 as the latter were originally provided on the gear circle 10. The gear teeth are formed integrally with, and project radially inwardly from, a root or base portion 33.

The arcuate outer peripheral surface of the segment 30 has a straight portion 34 which extends normal to the upper and lower surfaces of the gear segment, and a beveled surface 36 which extends between the surface 37 of the segment and the straight surface 34 and is inclined at an angle of about 30 with respect to the straight surface 34. The outer periphery of each of the segments 30 is formed on a radius of curvature which is slightly greater than the radius of curvature of a circle drawn through the root or base of the old gear teeth 16 on the gear circle 12. Stated differently, the outer peripheral edge of the segments 30 is formed on a figure of revolution which lies somewhere between the base of the teeth 16 on the gear circle 10 illustrated in FIGURE 1, and the upwardly extending leg 24 of the brace 22. Dimensioning the segments 30 in this way assures that they may be easily joined to the gear circle 16 after a portion thereof has been removed in the manner hereinafter described, even though the gear circle may be substantially distorted from its original true circular configuration.

In forging the preformed segments 30, more expensive metals of greater hardness and improved durability can be used for forming the segments and their associated teeth 32 than are generally employed in originally fabricating the entire gear circle 10. The number of the segments 30 formed, and the arcuate length of the segments may, as has been already suggested, be varied, but preferably, each segment corresponds to an octant of the gear circle which is to be rebuilt. The selection of an octant, or 45 of arc, as the lineal dimension of the segment 30 is based upon the usual number of 64 teeth which are provided on the gear circles of motor graders, a number evenly divisible by 8-and also upon the fact that, if the segments are made larger than an octant, casting of the segments as a true segment of a circle with the teeth perfectly formed becomes more ditficult and expensive.

In preparing to remove the old WOI'H or fractured gear teeth 16 from the gear circle 10, a plurality of slots are initially cut in a radial direction from the base of the teeth outwardly in the annular metallic member 12. These slots are spaced from each other around the periphery of the gear circle and are best illustrated in FIGURE 1. The slots can be suitably cut with a cutting torch, or by any other suitable method, and preferably include two opposed pairs of terminal slots 40 which are cut from the base of the teeth radially outwardly in the annular metallic member 12, and are separated or spaced from each other by two of the gear teeth. In other words, each of the terminal slots 40 in each of the pairs of these slots are separated by a pair of the gear teeth 16, and the two pairs of slots 40 are disposed from each other around the gear circle. The purpose of these terminal slots 40 will become clear as the discussion is subsequently developed.

Positioned at equally spaced intervals around the gear circle 10 are additional slots 42 which will be termed indexing or reference slots. Preferably, six of the reference slots 42 are formed or cut into the annular metallic member 12 of the gear circle and are spaced about 45 from each other, or from the terminal slots 40 as the case may be. All of the terminal slots 40 and reference slots 42 are of equal radial length.

When the terminal slots 40 and reference slots 42 have been cut in the gear circle 10, a disc-shaped metallic cutting jig 44 is lowered to the top of the gear circle 10 and rests on the upper surface thereof. A pad eye or closed loop 46 is secured in the center of the top of the cutting jig 44, and is used to lower the jig into position on top of the gear circle. The disc-shaped cutting jig 44 is provided with a perfectly round outer peripheral edge 48 and has a portion thereof cut away adjacent the outer peripheral edge 48 to form a flat, upwardly facing annular surface 50 which extends between the outer peripheral edge 48 and an upwardly projecting shoulder 52 formed on the upper surface of the cutting jig. Radially inwardly from the shoulder 52 are a pair of concentric annular slots or grooves 54 which are concentric with respect to each other and with respect to the outer peripheral edge 48 of the jig. Disposed at circumferentially spaced intervals around the cutting jig 44 in the flat upwardly facing surface 50, thereof, are a plurality of threaded, cap screwreceiving apertures 56. These apertures are used conjunctively with cap screws and clamping blocks as hereinafter described for retaining the new, preformed gear segments in place during a later stage of .the process of the invention.

When the disc-shaped cutting jig 44 has been placed in position on the upper surface of the gear circle 10, it is centrally positioned thereon by the use of the reference slots 42 and the terminal slots 40. The function of these slots is to permit the cutting jig to be symmetrically and centrally positioned on the gear circle 10, even though the gear circle may be distorted into a slightly elliptical configuration. All of the slots 40 and 42 are of the same depth, and by placing the cutting jig 44 on the gear circle so that slots diametrically opposed from each other across the cutting jig are covered by the jig to the same extent, the symmetrical positioning of the jig on top of the gear circle is assured. In :this way, when the several preformed segments 30 are mounted in position inside the gear circle 10 in place of the removed teeth, as hereinafter described, the segments will be symmetrically positioned within the gear circle, even though the gear circle may be slightly distorted from a truly circular configuration.

With the cutting jig resting on top of the gear circle 10 in the position illustrated in FIGURES 2 and 4, an automatic flame cutting machine, such as the N-C-G Cut- O-Matic, manufactured by National Cylinder Gas Co., a division of Chemtron Corporation, of 840 North Michigan Avenue, Chicago, Illinois, is mounted on the upper surface of the cutting jig with its rollers or wheels 57 positioned in at least one of the annular grooves 54 so that the main body 58 of the flame cutting machine moves about the cutting jig in a circle as the wheels 57 guide in and move along the groove 54. A cutting head 60 is provided on a flame cutting machine of the type described, and can be adjusted in its horizontal spacing from the body 58 of the machine, and also in the angle which the cutting head and cutting flame which emanates therefrom makes With respect to the vertical. Thus, as illustrated in FIGURES 3 and 4, the cutting head 60 is adjusted in its angular setting, and in its horizontal spacing from the body 58 so as to cut through the annular metallic member 12 of the gear circle 10 along a circular line which is spaced radially outwardly from the outer peripheral edge 48 of the cutting jig 44 by about one inch. The angle of the cutting head 60 also assures that it will cut through the annular metallic member 12 so as to form a beveled surface extending at an angle of about 15 with respect to the vertical (75 with respect to the upper surface of the annular metallic member 12) as best illustrated in the sectional views shown in FIGURES 3 and 10 of the drawings.

Cutting is commenced at one of the terminal slots 40 and proceeds in a circumferential direction around the gear circle 10 away from the other terminal slot in the pair. Thus, when the cutting head 60 has traveled from one of the terminal slots 40 to the next adjacent reference slot 42, a segment of the old gear teeth 16 will be cut away from the root or base portion constituted by the annular metallic member 12, and can 'be removed from the gear circle 10. Cutting proceeds around the gear circle 10 with the several segments of teeth defined between the reference slots 42 being removed in sequence. When the terminal slot 40 on the opposite side of the gear circle from the terminal slot 40 at which the cutting was commenced is reached, the cutting head is moved across to the next adjacent terminal slot 40 so as to leave the two intervening gear teeth 16 in place. This permits these two teeth to continue to function as a support for the cutting jig 44 until the cutting operation is completed. Cutting with the flame is recommenced at the next adjacent terminal slot and continued around the gear circle through the several reference slots 42 until the terminal slot 40 adjacent the terminal slot 40 where the cutting operation was started is reached. As a final step in removing the old and worn teeth '16 from the gear circle 10, the cutting jig 44 may be supported by other means than the gear circle 10, and the two teeth 16 located between each pair of the terminal slots 40 then removed by cutting through the gear circle at the same angle, or, alternatively, the cutting jig may be entirely removed from the gear circle, and the remaining four teeth between the two pairs of terminal slots 40 removed by a welder using a cutting torch.

In the next step of the process, with the cutting jig 44 positioned with its machined upper surface facing upwardly, and the flame cutting machine removed therefrom, the eight preformed, toothed segments 30 are placed on the upwardly facing flat surface around the jig with the radially inner ends of the several teeth 32 abutting against the upwardly extending shoulder 52. The shoulder 52 is perfectly circular in configuration, and the inner ends of the teeth 32 are also formed on a circle so that the segments are aligned with each other on the periphery of a perfect circle. The length of the segments 30 is such that a small space is provided therebetween as illustrated in FIGURE 8. This accommodates a certain amount of thermal expansion in the circular direction of the part of the segments when they are welded to the gear circle 10 as hereinafter described.

When the preformed arcuate segments 30 have been positioned around the cutting jig 44 with their teeth 32 abutting the upwardly extending shoulder 52, they are clamped in this position by a plurality of clamping blocks as illustrated best in FIGURE 8. Each of the clamping blocks 60 is elongated and has a flat lower surface for abutting flatly against the upper surface of the respective arcuate gear segment 30. A cap screw 62 is extended downwardly through a hole formed in each of the clamping blocks 60 and engages one of the internally threaded cap screw apertures 56 which are located in circumferentially spaced relation around the cutting jig 44 in the fiat upwardly facing surface 50. The clamping blocks 60 and cap screws 62 function to retain the arcuate toothed segments 30 in their exact positions around the cutting jig 44 as illustrated in FIGURE 8 with a small circumferential spacing provided between adjacent segments.

When the arcuate segments 30 have been clamped in position around the periphery of the cutting jig 44, the jig is lifted upwardly and is inverted so that the segments 30 carried on the machined surface of the jig face downwardly. The jig 44 carrying the segments is then lowered into position Within the gear circle 10 from which the old teeth have been removed so that it occupies the position depicted in FIGURE 9. Lowering of the inverted jig 44 can be suitably accomplished with a pad eye or hook 66 similar to the hook 46 disposed at the center of the machined face of the jig on the opposite side thereof.

When the jig is positioned within the annular metallic member 12 of the gear circle 10 as illustrated in FIG- URE 9, the jig is then leveled in a horizontal plane by the use of leveling plates 68, and vertically extending leveling screws 70. It will be noted in referring to FIG- URE 9 that four of the leveling plates 68 are disposed around the periphery of the cutting jig 44 in equally spaced circumferential relation to each other, and are bolted or otherwise suitably secured to the face of the jig by 'bolts 72 or other suitable means, thus permitting the leveling plates to be quickly detached from the jig. The leveling screws 70 can be screwed through the leveling plates 68 to any extent desired, and a spirit level or any other suitable means is then used to bring the jig 44 and the arcuate segments 30 into a horizontal plane.

1 l The gear circle has already been positioned in as nearly a horizontal plane as possible prior to the lower end of the cutting jig 44 and the segments carried thereby into the interior of the gear circle, but because of possible distortions from the horizontal plane which may characterize the gear circle after extended periods of use, the leveling techique utilizing the leveling plates 68 and leveling screws 70 is preferably followed to assure that when the preformed segments 30 are welded to the gear circle as hereinafter described, they will extend in a substantially horizontal plane.

When the cutting jig 44 and the preformed arcuate toothed segments 30 secured thereto are positioned within the gear circle 10 in the manner described in the preceding paragraph, the assembly appears in cross-section as illustrated in FIGURE 10 of the drawings. It will thus be noticed that a gap exists between the outer peripheral edge of each of the segments 30 and the tapered or beveled surface forming the inner periphery of the annular metallic member 12 of the gear circle 10.

With the cutting jig 44 and the segments 30 carried thereby horizontally beveled, each of the segments is tackwelded to the gear circle face. This is accomplished by tack-welding the segments on opposite sides of the ring from each other in a staggered sequence in order to reduce distortion resulting from unbalanced stresses as the segments and gear circle are heated. The tack-weld material is placed in the gap, g, formed between the beveled surface on the inner periphery of the annular metallic member 12 of the gear circle 10, and the straight surface 34 of each of the gear segments. The gap, g, is illustrated in FIGURE 9. After the tack-welding of the segments has been completed, a continuous bead of weld material is placed in the described gap, g, between the segments and the gear circle 10 completely around the outer periphery of all of the segments. Formation of the bead should also be accomplished by welding in a staggered sequence around the periphery of the gear circle.

The cutting jig 44, arcuate segments 30 and the gear circle 10 are then all inverted and rested flatly on the ground or other surface as depicted in FIGURE 11. If desired, and to permit more room for welding, the clamping blocks 60 and cap screws 62 may then be removed since the arcuate segments 30 are retained in position by the welding to the upper side of the gear circle 10 which has already been accomplished. The gap, g, which exists between the tapered peripheral surface 36 of each of the gear segments and the beveled surface on the inner periphery of the annular metallic member 12 of the gear circle 10 is then filled with weld metal. When the welding has been completed, the gear circle 10 with the new teeth carried by the arcuate segments 30 secured thereto is permitted to cool before the cutting jig 44 is removed. This assures that shrinkage and distortion which may tend to occur during cooling of the assembly will not cause the joined segments to become distorted from a truly circular configuration. After the jig 44 has been removed, excess weld metal may be ground away to provide finished surfaces at the points of junction of the segments 30 with the annular metallic member 12 of the gear circle 10. The gear circle 10 is now ready for replacement on the motor grader, and the new teeth which are provided will be in perfectly circular array even though the annular metallic member 12 may remain distorted to some extent.

The method of the present invention has the advantage of incorporating a new, truly circular inner peripheral portion in the outer peripheral portion of an old gear circle so as to provide new teeth of stronger, more durable metal. The portion of the gear circle which is of greatest mechanical strength is the outer portion by reason of the inclusion thereon of the flange 18 and brace 22. Since this port-ion of the gear circle has already undergone distortion, it is unlikely that the gear circle, provided it is reinstalled in its same relative position to the grader blade which it carries, and which relative. position it occupied prior to removal, will undergo much, if any, further distortion. Thus, the new inner peripheral portion, including the new teeth 32 will resist distortion, and will remain of true circular configuration for most or all of the remaining operating life of the entire gear circle. The operation of replacing the worn or fractured teeth can be accomplished by a person of relatively little technical skill or training, and can be accomplished in less time than would be required to replace the worn teeth in an individual manner.

Although a preferred method of practicing the present invention has been hereinbefore described, it will be understood that certain steps, procedures and materials described are to be considered equivalent to others not disclosed. Insofar, therefore, as any practice of the invention disclosed herein, whether authorized or unauthorized, employs steps and materials which are to any degree equivalent or analogous to the steps and materials herein disclosed, it is intended that such practices of the method of the invention shall be circumscribed and dominated by the appended claims except as such claims may be construed to be necessarily limited.

What is claimed is:

1. A method of replacing worn gear teeth on a gear circle of the type having an annular metallic member enclosing a free, unobstructed space, said annular metallic member having radially inwardly extending gear teeth at the inner periphery thereof, said method comprising:

forming a plurality of toothed, metallic arcuate segments each having an outer periphery having a radius of curvature greater than the radius of curvature of a circle drawn through the points of connection of the teeth of said gear circle to said annular metallic member, each of said segments having teeth of identical pitch to those carried by said gear circle, and said segments collectively forming a circle when placed in substantially end-to-e-nd relationship to each other;

cutting away all of the gear teeth from said gear circle by cutting through said gear circle along an annular reference line having a radius larger than the radius of curvature of the outer periphery of said arcuate segments;

positioning said arcuate segments in en'd-to-end circular array inside the outer peripheral portion of said gear circle in place of the removed inner peripheral portion thereof; and

securing said arcuate segments to said outer peripheral portion of the gear circle while maintaining the circular array of said segments.

2. The method claimed in claim 1 wherein said metallic arcuate segments are formed using a harder, more durable metal to form the teeth on said segments than that used in the original teeth of the gear circle.

3. The method claimed in claim 1 wherein said gear circle is from four to seven feet in diameter and wherein said segments are each equivalent to an octant of the circle formed by joining said segments together in end-t0- end relation.

4. The method claimed in claim 1 wherein the gear teeth are cut away from said gear circle by concentrically superimposing a disc-shaped cutting jig over said gear circle, and

moving an automatic flame cutting machine around said disc-shaped cutting jig adjacent the outer periphery thereof on annular guide means on said cutting jig while directing the flame from said flame cutting machine against the gear circle along said annular reference line.

5. The method claimed in claim 4 wherein said segments are positioned in said circular array inside the outer peripheral portion of said gear circle by supporting said segments in end-to-end relation on the outer peripheral portion of said cutting jig with the outer periphery of each of said segments spaced out- 13 wardly from the outer peripheral edge of said cutting jig by a distance less than the distance separating the outer peripheral edge of said cutting jig from said annular reference line during said flame cutting operation; then lowering said disc-shaped cutting jig with the segments supported thereon into said gear circle. 6. The method claimed in claim wherein said segments are secured to the outer peripheral portion of said gear circle while maintaining the circular array of said segments by 4 tack-welding each segment to the outer peripheral portion of said gear circle while supporting said segments on said cutting jig within said gear circle; and

substantially filling the space between said segments and the outer peripheral portion of said gear circle with weld metal. 7. The method of replacing worn and defective teeth on motor grader gear circles comprising:

forming a plurality of toothed, arcuate segments identical in configuration to each other and to corresponding arcuate segments of the gear circle upon which are located the worn and defective teeth to be replaced, as such corresponding arcuate segments were configured at the time the gear circle was new, said newly formed segments being segments of a true circle; forming a plurality of equal length radially outwardly extending reference slots in the gear circle with said slots being spaced at substantially equal circumferential intervals around the gear circle;

superimposing on the gear circle so as to partially cover said reference slots, a disc-shaped cutting jig having a perfectly circular outer periphery formed on a radius intermediate in length between the radii of the inner and outer peripheries of the gear circle;

using the reference slots to symmetrically center the cutting jig on said gear circle;

using the outer periphery of the cutting jig to provide a circular reference line for cutting through said gear circle to remove the worn and defective teeth therefrom;

securing said arcuate segments to said cutting jig in circular array around the outer periphery thereof in a position to pass inside the outer peripheral portion of said gear circle from which the worn and defective teeth have been removed when said jig is lowered inside said gear circle;

lowering the cutting jig carrying the gear segments into said gear circle; and

securing said segments to said gear circle while they are maintained in circular array. 8. The method claimed in claim 7 wherein each of said arcuate segments is equivalent to an octant of the gear circle in its angular dimension.

9. The method claimed in claim 7 wherein when all of said segments are arranged in true circular array with their arcuate outer peripheries lying on a true circle, a space exists between adjacent segments whereby said segments may be welded to said gear circle to secure them thereto without detrimental eifect from thermal expansion.

10. The method claimed in claim 7 wherein said arcuate segments are formed using a harder, more durable metal to form the teeth on said segments than that used in the original teeth of the gear circle.

11. The method claimed in claim 7 wherein said segments are secured to said gear circle While maintaining the segments in circular array by tack-welding each segment to the outer peripheral portion of said gear circle while supporting said segments on said cutting jig within said gear circle; and

substantially filling the space between said segments and the outer peripheral portion of said gear circle with weld metal.

References Cited by the Examiner UNITED STATES PATENTS 2/1922 Troutner 29159.2 4/1963 Dawe et al 29--40l X 

1. A METHOD FOR REPLACING WORN GEAR TEETH ON A REAR CIRCLE OF THE TYPE HAVING AN ANNULAR METALLIC MEMBER ENCLOSING A FREE, UNOBSTRUCTED SPACE, SAID ANNULAR METALLIC MEMBER HAVING RADIALLY INWARDLY EXTENDING GEAR TEETH AT THE INNER PERIPHERY THEREOF, SAID METHOD COMPRISING: FORMING A PLURALITY OF TOOTHED, METALLIC ARCUATE SEGMENTS EACH HAVING AN OUTER PERIPHERY HAVING A RADIUS OF CURVATURE GREATER THAN THE RADIUS OF CURVATURE OF A CIRCLE DRAWN THROUGH THE POINTS OF CONNECTION OF THE TEETH OF SAID GEAR CIRCLE TO SAID ANNULAR METALLIC MEMBER, EACH OF SAID SEGMENTS HAVING TEETH OF INDENTICAL PITCH TO THOSE CARRIED BY SAID GEAR CIRCLE, AND SAID SEGMENTS COLLECTIVELY FORMING A CIRCLE WHEN PLACED IN SUBSTANTIALLY END-TO-END RELATIONSHIP TO EACH OTHER; CUTTING AWAY ALL OF THE GEAR TEETH FROM SAID GEAR CIRCLE BY CUTTING THROUGH SAID GEAR CIRCLE ALONG AN ANNULAR REFERENCE LINE HAVING A RADIUS LARGER THAN THE RADIUS OF CURVATURE OF THE OUTER PERIPHERY OF SAID ARCUATE SEGMENTS; 